FIG. 1 is a block diagram schematically illustrating principal elements of a reconfigurable optical add/drop multiplexer (ROADM) 2 known in the art. The ROADM 2 may be connected to send and receive optical dense wavelength division multiplexed (DWDM) signals. In FIG. 1, this connection is represented by an optical fiber span pair 4 connected to respective broadband optical ports 6 of the ROADM 2. However, it will be appreciated that, in many applications, optical routing and switching devices will be connected between the ROADM 2 and the fiber span pair 4, as will be described in greater detail below.
As may be seen in FIG. 1, the ROADM 2 may be provided as a set of modules 8-12 interconnected by optical fiber intra-node connections 14, 16. In the embodiment of FIG. 1, the modules forming the ROADM 2 comprise an amplifier module 8, a second-stage MUX/DeMUX module 10; and one or more first-stage MUX/DeMUX modules 12. The interconnections 14, 16 between these modules define a Drop path and a Add path of the ROADM 2.
The Drop path comprises a receive amplifier 18 in the amplifier module 8 for amplifying an inbound dense wavelength division multiplexed (DWDM) light (received through the input Broadband port 6a; a wavelength selective switch (WSS) 20 in the second-stage MUX/DeMUX module 10 for routing any selection of channels of the received DWDM light to any of a set of output fibers; and a power divider 22 of the first-stage MUX/DeMUX module 12 for receiving a respective one of the selections of channels, and supplying the light of these channels to a plurality of coherent receivers 24 (only one shown in FIG. 1).
The Add path generally mirrors the Drop path, by combining individual channel signals from a plurality of transmitters 26 into an outbound dense wavelength division multiplexed (DWDM) light that is output though the output broadband port 6b. In the embodiment of FIG. 1, the Add path comprises a respective power combiner 28, 30 in each of the first- and second-stage MUX/DeMUX modules 12, 10, and a launch amplifier 32 in the amplifier module 8. The first-stage power combiner 28 operates to combine light from a plurality of transmitters 26 (only one is shown in FIG. 1) onto a single fiber that is connected to the second-stage MUX/DeMUX module 10. When each of the transmitters 26 is tuned to emit light corresponding to a respective different narrow band wavelength channel, the light passed to the second-stage MUX/DeMUX module 10 will be a wavelength division multiplexed (WDM) light comprising each of the transmitted wavelength channels. The second-stage power combiner 30 operates to combine a plurality of channels' light (from respective first-stage power combiners 28) for transmission through the output broadband port 6b. The Add path amplifier 32 is coupled to output broadband port 6b, and operates to amplify the DWDM signal for transmission through downstream optical components, such as the optical fiber span 4.
The block diagram of FIG. 1 only shows a single first-stage MUX/DeMUX module 12 connected to the second-stage MUX/DeMUX module 10. However, it will be appreciated that there can be any number of first-stage MUX/DeMUX modules 12, up to the maximum number of inputs supported by the second-stage MUX/DeMUX module 10.
FIG. 2 is a block diagram illustrating a representative network node comprising a Directionally Independent Access (DIA) shelf 34 optically coupled to three fiber spans 4a-c via respective Optical Transmission Sections (OTSs) 36a-c. As may be seen in FIG. 2, the DIA 34 comprises the ROADM 2 of FIG. 1 coupled to a wavelength selective switch (WSS) 38 which is programmed to selectively switch channels between the ROADM 2 and each of the three OTSs 36. This arrangement combines Rx/Tx tunability with optical switching to enable the DIA 34 to add/drop channels to/from DWDM signals in any of three fiber spans 4a-c. The system shown in FIG. 2 has only one DIA 34 connected to three OTSs 36, whereas a typical network node may have more than one DIA shelf 34, each of which is connected to two or more OTSs 36.
With the introduction of multi degree ROADMs, combined with multiple DIAs and OTSs, the number and complexity of optical connections within a node becomes very high. For example, an 8 degree ROADM with two colorless DIA shelves can have over 600 fiber connections.
As nodal fiber configurations become increasingly complex, mechanical solutions are expected to become prevalent in order to improve fiber management. Many of these mechanical solutions will involve parallel optical cables (fiber ribbon cables). In this case it is critical that all fiber connections are validated before any traffic is placed on the system. For example, once a single fiber in a ribbon cable is in use, cleaning or moving any other fiber in the ribbon cable will not be possible without impacting traffic. This implies that all fiber connections must be thoroughly checked at the time of installation, even though they may not be used until a later date.
The increasing level of complexity in the physical fibering increases the likelihood that mistakes will be made during the installation and commissioning of optical equipment.
When deploying and commissioning optical systems, manual procedures are typically used to test and evaluate intra- and inter-node fiber connections. Although this provides the user of the equipment with the ability to evaluate physical connections, the testing is also prone to human error. As the complexity of the system increases, so too does the likelihood of errors in testing and evaluation process. Mistakes made during the commissioning and testing of equipment can go undetected, and result in failed service turn-ups for customers, which results in service delays and increased cost. Similar issues can be seen throughout the life cycle of optical equipment. Mistakes made during circuit pack replacements, regular maintenance, or capacity expansions can go undetected and result in service outages.
Techniques that enable improved speed and accuracy of testing and evaluation of optical equipment remain highly desirable.